This invention relates generally to watering devices for animals and more particularly concerns an automatic watering device which replenishes the water reservoir only after the reservoir is substantially emptied. The prior art has dealt with various types of watering devices for domestic house animals such as illustrated in U.S. Pat. No. 2,678,630 to R. O. Frederiksen. However, such patents have normally been of a demand type feeder wherein the animal must activate a ball or lever arm in order to release the water. Similarly, other watering tanks have been used for livestock. Examples are U.S. Pat. No. 2,570,694 to A. E. Langenbahm and U.S. Pat. No. 3,371,652 to R. A. Louks et al. Normally these devices have released a large quantity of water all at once into a watering trough, or a small amount of water is continually fed into the trough. At times, whenever a small amount of water has been drunk by the animal, the reservoir is immediately refilled.